Re: [pkix] EKU for intermediate certificates

Carl Wallace <carl@redhoundsoftware.com> Thu, 04 February 2016 18:00 UTC

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Date: Thu, 04 Feb 2016 13:00:29 -0500
From: Carl Wallace <carl@redhoundsoftware.com>
To: Peter Bowen <pzbowen@gmail.com>, Santosh Chokhani <santosh.chokhani@gmail.com>
Message-ID: <D2D8FB5B.4B529%carl@redhoundsoftware.com>
Thread-Topic: [pkix] EKU for intermediate certificates
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Subject: Re: [pkix] EKU for intermediate certificates
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On 2/4/16, 12:17 PM, "Peter Bowen" <pzbowen@gmail.com> wrote:

>The CA/Browser Forum sets standards for Certification Authorities.  It
>does not set requirements on implementers of path validation.

Does this mean there would be no issue with defining a flag to allow for
EKU semantics to be selected, since we now have two? Else we will rely on
folklore to know which implementations do what.

>
>That being said, many current web browsers and OS path validation
>libraries do enforce such constraints.  This includes Microsoft and
>Mozilla libraries, which underpin Internet Explorer, Edge, Firefox,
>and Chrome/Opera on Windows.
>
>Thanks,
>Peter
>
>On Thu, Feb 4, 2016 at 7:56 AM, Santosh Chokhani
><santosh.chokhani@gmail.com> wrote:
>> According the authors of the CABF criteria (I hope they will speak up),
>>the
>> intent of the language is not to make the enforcement of constraint on
>>the
>> certification path mandatory.
>>
>>
>>
>> They simply want the issuer to indicate limitations it imposes on the
>>CA.
>>
>>
>>
>> I am generally sympathetic to enforcement of the constraint on the path,
>> however this is a significant change to the semantics of the extension
>>and
>> path validation engine.
>>
>>
>>
>> From: pkix [mailto:pkix-bounces@ietf.org] On Behalf Of Carl Wallace
>> Sent: Thursday, February 4, 2016 8:14 AM
>> To: Koichi Sugimoto <koichi.sugimoto@globalsign.com>
>> Cc: pkix@ietf.org
>> Subject: Re: [pkix] EKU for intermediate certificates
>>
>>
>>
>> in the CAB Forum concept, if there any mechanism to indicate to a
>>compliant
>> validation engine that 5280 EKU semantics ought be used? Allowing a
>>toggle
>> probably beats simply changing the semantics of the extension for all
>>cases.
>>
>>
>>
>> From: pkix <pkix-bounces@ietf.org> on behalf of Koichi Sugimoto
>> <koichi.sugimoto@globalsign.com>
>> Date: Thursday, February 4, 2016 at 8:08 AM
>> To: "pkix@ietf.org" <pkix@ietf.org>
>> Subject: [pkix] EKU for intermediate certificates
>>
>>
>>
>> Hello.
>>
>>
>>
>> I hope the following definition should be changed.
>>
>>
>>
>>>4.2.1.12.  Extended Key Usage
>>
>>>
>>
>>>   This extension indicates one or more purposes for which the certified
>>
>>>   public key may be used, in addition to or in place of the basic
>>
>>>   purposes indicated in the key usage extension.  In general, this
>>
>>>   extension will appear only in end entity certificates.
>>
>>
>>
>>
>>
>> Now CABF (CA Browser Forum) specified Extended Key Usage as:
>>
>>
>>
>> P9:
>>
>> Technically Constrained Subordinate CA Certificate: A Subordinate CA
>> certificate which uses a
>>
>> combination of Extended Key Usage settings and Name Constraint settings
>>to
>> limit the scope within which the
>>
>> Subordinate CA Certificate may issue Subscriber or additional
>>Subordinate CA
>> Certificates.
>>
>>
>>
>> P34:
>>
>> ** Generally Extended Key Usage will only appear within end entity
>> certificates (as highlighted in RFC 5280
>>
>> (4.2.1.12)), however, Subordinate CAs MAY include the extension to
>>further
>> protect relying parties until the
>>
>> use of the extension is consistent between Application Software
>>Suppliers
>> whose software is used by a
>>
>> substantial portion of Relying Parties worldwide.
>>
>>
>>
>> P38-39:
>>
>> For a Subordinate CA Certificate to be considered Technically
>>Constrained,
>> the certificate MUST include an
>>
>> Extended Key Usage (EKU) extension specifying all extended key usages
>>that
>> the Subordinate CA Certificate is
>>
>> authorized to issue certificates for. The anyExtendedKeyUsage
>>KeyPurposeId
>> MUST NOT appear within this
>>
>> extension.
>>
>>
>>
>> Major browsers already support this specification, therefore, the next
>>RFC
>> should reflect this notation, I think.
>>
>> This notation is very important because we can restrict the range of
>> influence when end-entity certificates are
>>
>> unwillingly issued by attacks etc.
>>
>>
>>
>>
>>
>> Please see below:
>>
>> https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.3.2.pdf
>>
>>
>>
>>
>>
>> Regards,
>>
>> Koichi Sugimoto.
>>
>> _______________________________________________ pkix mailing list
>> pkix@ietf.org https://www.ietf.org/mailman/listinfo/pkix
>>
>>
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